1. Field of the Invention
The present invention relates to a thin-film electronic component and a motherboard, and more particularly to a thin-film electronic component and a motherboard, which are operated at high frequencies, suitably used for a thin-film capacitor, a thin-film inductor, a thin-film LC filter, a thin-film resistance, a thin-film RC filter, or the like.
2. Description of the Related Art
Accompanying the recent trend toward realizing electronic equipment in small sizes yet maintaining highly sophisticated functions, it has been strongly urged to provide electronic components having small size and slimness so that they can be installed in the electronic equipment to satisfy the demand for high-frequency use.
In a high-speed digital circuit of a computer that must process large quantity of data at high speeds, in particular, the clock frequency in a CPU chip is as high as from 200 MHz to 1 GHz, and the clock frequency of a bus among the chips is also as high as from 75 MHz to 133 MHz even on a level of a personal computer.
As the degree of integration of LSI increases and a larger and larger number of elements are provided in the chip, the power source voltage tends to be lowered to suppress electric power consumption. Accompanying an increase in the operation speed, an increase in the density, and a decrease in the voltage in the IC circuits, passive parts such as capacitors must also be designed in small sizes yet having large capacities to exhibit excellent characteristics for high-frequency pulses or high-speed pulses.
As the operation frequency increases, resistance and inductance possessed by the element cause an instantaneous drop in the power-source voltage on the side of the logic circuit, or new voltage noise. As a result, an error occurs on the logic circuit. In modern LSIs, in particular, the power source voltage has been lowered to suppress an increase in the consumption of electric power that results from an increase in the total number of elements, and the width of permissible change in the power source voltage has been decreased. During coming years, it is expected that there will be further increase in the number of elements and increase in the operation frequency, and consequently a reduction in resistance and inductance components on the mount portion will be of particular importance in connection with logic circuit errors.
As a natural consequence of such a trend, not only an improvement in the electrical characteristics of the passive element itself, but also mounting-related characteristics (mounting accuracy and mounting reliability) of higher level have been sought after. For example, higher mounting accuracy is required to cope with an increase in the number of the elements, and satisfactory reflow resistance is required for mounting components properly.
As a method for decreasing inductance in a connection portion of a capacitor, a thin-film capacitor is disclosed in U.S. Pat. No. 4,439,813. In this conventional thin film capacitor, to obtain electric signals fed from a lower electrode made of TiW, Ta, Al, and Cu in the shortest distance, a through hole is formed in an insulation layer, an upper electrode, and a protective layer, and, after forming a BLM layer made of Cr/Cu/Au on the inner wall of the through hole, a solder bump is formed on this BLM layer.
FIG. 6 shows the capacitor disclosed in this publication. On a supporting substrate 31, a lower electrode 33, an insulation layer 35, an upper electrode 37, and a protective layer 39 are stacked on top of one another. The lower electrode 33 is connected to an external terminal 41 via a through hole formed in the protective layer 39. The upper electrode 37 is connected to an external terminal 43 via a through hole formed in the protective layer 39. The external terminal 43 is formed on the insulation layer 35.
However, the above-described thin-film capacitor has the following disadvantage. In this construction, the insulation layer 35 is formed on the lower electrode 33 by a sputtering method, an evaporation method, or a sol-gel method. Since the lower electrode 33 is subjected to a high-temperature process, the adhesion strength between the supporting substrate 31 and the lower electrode 33 tends to be deteriorated. Therefore, when the external terminals 41 and 43, made of solder bumps, are coupled to the electrode disposed on a base, being fixed via the lower electrode 33 to the supporting substrate 31, the external terminals 41 and 43 tend to be stripped from the supporting substrate 31. This makes it impossible to attain adequate coupling strength between the thin-film capacitor and the base, with the result that the thin-film capacitor easily falls off due to some shock.
That is, the solder-bump external terminals 41 and 43 disposed via the lower electrode 33 on the supporting substrate 31 are put under unduly heavy load, and, when stripped off, breakage does not occur in the solder bump but occurs, for example, at the interface between the supporting substrate 31 and the lower electrode 33. Thus, it is impossible to make the most of the strength of the external terminal, i.e. solder bump, resulting in deterioration in the mounting reliability.
To overcome such an inconvenience, an adherent layer may be provided between the supporting substrate 31 and the lower electrode 33. In this case, however, the adherent layer is diffused or shifted due to the above-stated high-temperature process, and thus a desired function cannot be attained. As a result, the adhesion strength between the supporting substrate 31 and the lower electrode 33 is deteriorated.
An object of the invention is to provide a thin-film electronic component and a motherboard in which an external terminal is coupled to a supporting substrate with improved coupling strength.
The invention provides a thin-film electronic component comprising:
a supporting substrate;
a lower electrode formed on part of the supporting substrate;
an insulation layer formed on the lower electrode;
an upper electrode formed on the insulation layer;
a connection electrode formed on part of the supporting substrate located on a bottom surface of a through hole formed in the insulation layer, the connection electrode being electrically connected to the lower electrode; and
an external terminal disposed on the connection electrode within the through hole.
That is, the thin-film electronic component includes: a supporting substrate; a lower electrode formed on the supporting substrate; an insulation layer formed on the lower electrode; an upper electrode formed on the insulation layer; a connection electrode which is formed on a bottom surface of a through hole formed on the insulation layer and electrically connected to the lower electrode; and an external terminal disposed on the connection electrode within the through hole. In this construction, the connection electrode is disposed on the supporting substrate via a portion remaining free of the lower electrode. In other words, the inside of the through hole formed in the insulation layer serves as a region free of the insulation layer (insulation layer-free region), and the connection electrode provided within the insulation layer-free region is disposed on the supporting substrate via the portion free of the lower electrode.
Adopting such a structure confers the following advantages. Even if the insulation layer is formed by the sputtering, evaporation, or sol-gel method and the lower electrode is subjected to a high-temperature process, since the connection electrode is fabricated and disposed on the supporting substrate after completion of the formation of the insulation layer, it is possible to attain adequate coupling strength between the supporting substrate and the connection electrode disposed directly, or via an adherent layer, on the supporting substrate. This helps increase the coupling strength between the supporting substrate and the external terminal electrically connected via the connection electrode to the lower electrode, thereby improving the mounting reliability.
In the thin-film electronic component of the invention, it is preferable that the connection electrode and the lower electrode are superposed on each other at an inner periphery of the bottom surface of the through hole. This arrangement ensures that the connection electrode and the lower electrode are electrically connected to each other.
In the thin-film electronic component of the invention, it is preferable that an area of a region where the connection electrode and the lower electrode are mutually superposed is set to fall in a range of 1 to 10% of a cross-sectional area of the through hole. This arrangement helps improve the coupling strength of the external terminal to the supporting substrate and ensures that the connection electrode is electrically connected to the lower electrode.
The motherboard embodying the invention is designed to have the above-described thin-film electronic component mounted on the surface of its base via the external terminal. In this motherboard, sufficiently high coupling strength can be ensured between the external terminal and the supporting substrate, thereby improving the coupling strength between the base and the thin-film electronic component which is coupled via the external terminal to the base.
The invention further provides a thin-film electronic component comprising:
a supporting substrate;
a lower electrode formed on the supporting substrate;
an insulation layer formed on the lower electrode;
an upper electrode formed on the insulation layer;
a connection electrode electrically connected to the lower electrode;
an external terminal electrically connected to the connection electrode; and
the insulation layer having a first through hole so as for the lower electrode to be exposed;
wherein the lower electrode exposed through the first through hole has a second though hole so as for the supporting substrate to be exposed,
and wherein the connection electrode is so formed as to make contact with the supporting substrate exposed through the second through hole and the lower electrode exposed through the first through hole.
According to the invention, since the connection electrode, which is formed after formation of the insulation layer, is disposed directly on the supporting substrate, without the lower electrode interposed therebetween that has undergone a high-temperature process, it never occurs that the adhesion strength between the connection electrode and the supporting substrate is deteriorated. Therefore, satisfactory adhesion strength can be secured in the solder-bump external terminal disposed on the supporting substrate via, for example, a solder adherent layer, a solid barrier layer, and the connection or upper electrode. This makes it possible to make the most of the strength of the external terminal.